HTML (Hyper Text Markup Language) mainly used in the World Wide Web system is text data made up of tags surrounded by “<” and “>” and character data. This HTML allows description of multimedia documents containing texts and image data, and has been widely used and developed with the spread of the Internet.
The initial HTML simply laid out text data and image data in the display area of a display program called a browser. With the spread after that, however, the HTML has been extended to express more complicated layouts. This extension is presently organized as style sheets by W3C (World Wide Web Consortium). For example, style sheet standards such as CSS (Cascade Style Sheet) and XSL (Extensible Stylesheet Language) exist.
This W3C also defines XHTML obtained by redefining HTML by XML (Extensible Markup Language).
It is presently possible, by combining HTML/XHTML/XML and style sheets (e.g., CSS), to express layouts which could not be expressed by the initial HTML, e.g., to overlap graphic objects such as character strings, images, and rectangles visualized by using font data.
The W3C further defines various standards such as SMIL and SVG. The former is a multimedia document description system primarily for the purpose of presentation, and has description capability particularly in the time axis direction. The latter is a vector graphics description system and capable of describing more complicated layouts substantially equivalent to PDL (Page Description Language).
Data obtained by any of the above description systems is described in a text data form. For non-text data such as an image, only reference to the image file is described (Hyper Link). To display, e.g., HTML data, a browser first loads the HTML data, and determines and visualizes a layout by analyzing tags. If reference to non-text data such as an image is contained in this HTML, the browser acquires and displays the whole of the image file (or another non-text data) in accordance with the reference contained in the HTML, after or simultaneously with interpretation of the HTML.
This image file is transferred in accordance with a protocol described in a URL (Uniform Resource Locator) designated by the HTML or Hyper Link to the image data. The most general protocol is HTTP (Hyper Text Transfer Protocol). When this HTTP is used, a client designates a virtual path name and file name of a target file on a server, and the server specifies the file entity from the virtual path name and file name designated by the client, and transmits the whole file to the client.
On the other hand, if an image has a Flashpix image format (“Flashpix Specification 1.0”, I3A), IIP (“Internet Imaging Protocol version 1.06”, Digital Imaging Group) is known as a method of communicating a partial image of the image. The Flashpix image format holds an image at plurality of resolutions (each resolution image has a resolution ½ that of an immediately higher resolution image). In addition, the Flashpix image format segments each resolution image into partial images called tiles each having 64×64 pixels, and holds these images in a file in a form by which each tile image can be accessed. The IIP is a protocol packaged on the HTTP and can acquire a target partial image for each tile by transmitting the URL of a target Flashpix image file, a target resolution image, and the tile identifier of a tile corresponding to a target area in the resolution image.
As described above, the present multimedia data description systems can describe complicated layouts, e.g., a layout in which one graphic object overlaps another graphic object. In this case, data of the overlapped portion of the underlying graphic object has no influence on the layout generated as a result. If the underlying graphic object is an image, the present HTTP acquires even data of a portion not contributing to the final layout. Therefore, if the line speed between the server and client is low or if the communication is charged, the communication time or communication fee undesirably exceeds the originally necessary time or fee.
To prevent this, when creating multimedia data, the author may predict the final layout and form a layout having no overlap by segmenting an image into a plurality of image data in advance. However, this method still has the following problems.    (1) Specifications of the current standards of HTML/XHTML and style sheets are ambiguous and depend on an interpreter (e.g., a browser). Therefore, a layout actually determined by a target interpreter does not match the prediction by the author in some cases.    (2) Conflicts occur if a layout dynamically changes, e.g., if the size of image data to be referred to or an overlying graphic object changes each time, of if an interpreter can dynamically change the layout of graphic objects.
As processing for overlapping of graphic objects as described above, methods described in Japanese Patent Laid-Open Nos. 8-251391 and 10-21020 are known. The former method determines overlapping of image data when PDL interpretation is performed by a page printer or the like. If a graphic object overlaps an image object, the image is segmented, and image data in a portion covered with the other graphic object is deleted, thereby saving the memory. The latter method deletes a graphic object instruction completely covered with another graphic object, thereby reducing the load of a subsequent drawing process. Unfortunately, either processing is performed after graphic object data (image data if the object is an image) to be deleted is received, and hence does not contribute to reduction of the communication time described above.